The problem that Mr Cameron has introduced for the Tories is this:
People who "always vote Labour" (such as most of those in South Wales, Southern Scotland,the big conurbations in Northern England, and Inner London) will never vote Tory. He has no possibility of gaining voters from theose areas no matter what Labour has done in the past or promises to do in the future. Because of the Coalition's abysmal record over the past two years Tory voters are now looking elsewhere and many are turning to UKIP. All this does is strengthens Labour's position.
The Coalition has been a disaster for the UK and for Tory voters in particular. Their interests are nor being addressed. On the contrary, despite Labour's rhetoric about "millionaires" being pampered by the Tories, even if this is true, millionaires make up a very small proportion of Tory voters. The vast majority are "comfortable" and the Tories squirm at the thought of that comfort.
My own view is that the sooner the Coalition is ended the better it will be for the entire UK. But of course because of the outrageous "fixed term Parliament Bill" introduced soon after the 2010 election, this is unlikely to happen.